CN112666435B - Insulation detection design method of automobile charging system facing booster circuit - Google Patents
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Abstract
The invention relates to the field of insulation detection of power systems, and discloses an insulation detection design method of an automobile charging system facing a booster circuit. The method comprises the following steps: the method comprises the steps of respectively selecting a first equivalent resistor of a positive input end of a booster circuit to the ground, a second equivalent resistor of a negative input end of the booster circuit to the ground and a resistance value of a third equivalent resistor of a negative output end of the booster circuit to the ground in advance, simultaneously obtaining a boosted voltage of the booster circuit, detecting influences of a fourth equivalent resistor of the positive output end of the booster circuit to the ground on voltages at two ends of the first equivalent resistor and voltages at two ends of the second equivalent resistor through simulation experiments, determining a value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero according to results of the simulation experiments, and selecting the resistance value of the fourth equivalent resistor in the value range. Based on the method, the influence of the insulation resistance to ground on the subsequent measurement is considered when the booster circuit is designed, so that the compatibility and the accuracy of the subsequent insulation resistance measurement are ensured.
Description
Technical Field
The invention relates to the technical field of insulation detection of power systems, in particular to an insulation detection design method of an automobile charging system facing a booster circuit.
Background
The insulation problem of electrical equipment in the electrical industry is a main factor causing the electrical equipment to fail, the higher the insulation degree is more beneficial to the safety of the electrical equipment, and the quality of the insulation performance has a certain influence on the service life of the electrical equipment. In the current electric automobile industry, in order to make the electric equipment work normally, the electric equipment is not frequently failed to ensure the safe and stable operation of the electric power system, the insulation state of the electric equipment is checked regularly by the insulation detection equipment IMD (Isolation Monitoring Device), so that the IMD detection becomes an important work in the electric equipment inspection.
The insulation resistance of the positive and negative direct current buses of the direct current charging of the electric automobile to the ground can reflect the insulation state of the electric equipment to a great extent, the insulation resistance is an important index for judging the insulation performance of the electric equipment, and the method for detecting the insulation state of the electric equipment in an auxiliary way is very popular in the electric automobile because the insulation resistance is measured by a relatively simple and convenient auxiliary test method. The insulation resistance is not always maintained at a constant value but is changed to some extent under the influence of the environment, so that it is necessary to detect the insulation resistance at a fixed timing.
Referring to fig. 1a to 1c, fig. 1a to 1c are schematic diagrams of an insulation resistance detection method based on an unbalanced bridge principle. As shown in fig. 1a to 1c, rx is the insulation resistance of the positive dc bus to the ground, ry is the insulation resistance of the negative dc bus to the ground, by switching in the known resistance at the two ends of Rx and detecting the voltage at the two ends of Rx, respectively, switching in the known resistance at the two ends of Ry and detecting the voltage at the two ends of Ry, in the case that the voltage at the two ends of the positive dc bus is determined, the resistance of Rx and Ry can be obtained by establishing an equation:
in equations 1 and 2, UDC is the voltage across the positive and negative dc bus, ux is the equivalent insulation resistance of the positive dc bus to ground, uy is the equivalent insulation resistance of the negative dc bus to ground, and R is the known cut-in resistance.
As can be seen from the above formulas 1 and 2, the test result Rx/Ry depends on the sampling accuracy of the voltage, and if the measured voltage has zero, the Rx/Ry will have poles, which results in very inaccurate Rx/Ry test results, and if the cut-in resistor R has an incorrect value, it may cause Rx/Ry to have a certain error or affect the stability of the current loop control. Therefore, the insulation resistance obtained by IMD detection in the related art is not accurate enough.
Disclosure of Invention
In order to solve the technical problems, the embodiment of the invention provides an insulation detection design method of an automobile charging system for a booster circuit, which can solve the technical problem that an insulation resistance detection circuit has failure risk in the related technology for the booster circuit.
The embodiment of the invention provides the following technical scheme for solving the technical problems:
in a first aspect, an embodiment of the present invention provides an insulation detection design method for an automobile charging system facing a boost circuit, where the automobile charging system includes a rechargeable battery and a boost circuit, an output end of the boost circuit is electrically connected to the rechargeable battery, and an input end of the boost circuit is electrically connected to a charger, and the method is characterized in that the method includes: pre-selecting the resistance value of a first equivalent resistor of the positive input end of the booster circuit to the ground; pre-selecting the resistance value of a second equivalent resistor of the negative input end of the booster circuit to the ground; and the resistance of the third equivalent resistor of the negative output end of the booster circuit to the ground; determining a boosted voltage between a positive output end and a negative output end of the booster circuit; through a simulation experiment, detecting the influence of the resistance value of a fourth equivalent resistor of the positive output end of the booster circuit on the ground equivalent resistor on a first voltage and a second voltage, wherein the first voltage is the voltage at two ends of the first equivalent resistor, and the second voltage is the voltage at two ends of the second equivalent resistor; according to the result of the simulation experiment, determining the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero; and selecting the resistance value of the fourth equivalent resistor in the value range.
Optionally, the step of selecting the resistance value of the fourth equivalent resistor in the value range further includes: and selecting the resistance value of a fourth equivalent resistor corresponding to the maximum voltage of the first voltage and the second voltage deviating from the zero point within the value range according to the result of the simulation experiment.
Optionally, the method further comprises: determining an error coefficient; correcting the result of the simulation experiment according to the error coefficient; and determining the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero according to the result of the simulation experiment, wherein the step specifically comprises the following steps: and determining the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero according to the corrected simulation experiment result.
Optionally, the resistance of the first equivalent resistor, the resistance of the second equivalent resistor and the resistance of the third equivalent resistor are all values meeting the preset insulation resistance to ground test standard of the automobile charging system.
Optionally, the automobile charging system further comprises a first change-over switch and a second change-over switch; one end of the first change-over switch is used for being electrically connected with the positive electrode of the charger, and the other end of the first change-over switch is electrically connected with the positive input end of the boost circuit; one end of the second change-over switch is used for being electrically connected with the negative electrode of the charger, and the other end of the second change-over switch is electrically connected with the negative input end of the boost circuit.
Optionally, the automobile charging system further comprises a third change-over switch and a fourth change-over switch; one end of the third change-over switch is electrically connected with the positive output end of the boost circuit, and the other end of the third change-over switch is electrically connected with the positive electrode of the rechargeable battery; one end of the fourth change-over switch is electrically connected with the negative output end of the boost circuit, and the other end of the fourth change-over switch is electrically connected with the negative electrode of the rechargeable battery.
Optionally, the automobile charging system further comprises a first fuse and a second fuse; one end of the first fuse is electrically connected with the positive input end of the booster circuit, the other end of the first fuse is electrically connected with the positive electrode of the rechargeable battery, one end of the second fuse is electrically connected with the negative input end of the booster circuit, and the other end of the second fuse is electrically connected with the negative electrode of the rechargeable battery.
Optionally, the automobile charging system further comprises a first detection unit, a second detection unit and a controller; the first detection unit is used for detecting first voltages at two ends of the first equivalent resistor, the second detection unit is used for detecting second voltages at two ends of the second equivalent resistor, and the controller is respectively connected with the first detection unit and the second detection unit and used for acquiring data of the first voltages and the second voltages.
Optionally, the first detection unit includes a first voltage detection circuit, a first switching resistor and a first switch; the first voltage detection circuit and the first change-over switch are connected with the controller, the first switching-in resistor and the first change-over switch are connected in series and then connected with the first equivalent resistor in parallel, and the first voltage detection circuit is used for detecting the first voltage and transmitting the first voltage data to the controller.
Optionally, the second detection unit includes a second voltage detection circuit, a second switching resistor and a second switch; the second voltage detection circuit and the second change-over switch are connected with the controller, the second cut-in resistor and the second change-over switch are connected in series and then connected with the second equivalent resistor in parallel, and the second voltage detection circuit is used for detecting the second voltage and transmitting the second voltage data to the controller.
The embodiment of the invention has the beneficial effects that: the insulation detection design method of the automobile charging system facing the booster circuit is provided. The method comprises the following steps: for an automobile charging system with a boost circuit, the first equivalent resistor of the positive input end of the boost circuit to the ground, the second equivalent resistor of the negative input end of the boost circuit to the ground and the resistance value of the third equivalent resistor of the negative output end of the boost circuit to the ground are selected in advance, the boost voltage of the boost circuit is obtained at the same time, the influence of the fourth equivalent resistor of the positive output end of the boost circuit to the voltage at two ends of the first equivalent resistor and the voltage at two ends of the second equivalent resistor is detected through a simulation experiment, the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero is determined according to the result of the simulation experiment, and the resistance value of the fourth equivalent resistor is selected in the value range. Based on the method, the influence of the insulation resistance to ground on the subsequent measurement is considered when the booster circuit is designed, so that the compatibility and the accuracy of the subsequent insulation resistance measurement are ensured.
Drawings
One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to be taken in a limiting sense, unless otherwise indicated.
FIGS. 1 a-1 c are schematic diagrams of an IMD detection method based on the unbalanced bridge principle;
fig. 2 is a schematic structural diagram of a charging system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an embodiment of an automobile charging system;
FIG. 4 is a schematic diagram of an automobile charging system according to another embodiment of the present invention;
fig. 5 is a schematic flow chart of an insulation detection design method of an automobile charging system facing a boost circuit according to an embodiment of the invention;
FIG. 6 is a graph of simulation experiment results based on the method of FIG. 5;
FIG. 7 is a diagram of simulation experiment results for verifying the effectiveness of the fourth equivalent resistor;
FIG. 8 is a graph of results of another simulation experiment to verify the effectiveness of the fourth equivalent resistance;
fig. 9 is a schematic structural diagram of an automobile charging system according to another embodiment of the present invention.
Detailed Description
In order to facilitate an understanding of the present application, the present application will be described in more detail below with reference to the accompanying drawings and detailed description. It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used in this specification includes any and all combinations of one or more of the associated listed items.
In addition, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not collide with each other.
Currently, the mainstream electric automobile is also a 400V architecture, in which a charging voltage of a rechargeable battery is 400VDC, and a charger supporting a 400V output voltage is used for charging. As more and more electric vehicles are introduced in the market, an 800V architecture technology is gradually mentioned, the charging voltage of the rechargeable battery in the architecture is 800V, if a charger supporting the highest 400V output voltage is used in the architecture, the charging requirement of the rechargeable battery cannot be obviously satisfied, so, in order to be compatible with the charger with the lower output voltage, a boost circuit is generally added between the output of the charger and the rechargeable battery, the boost amplitude of the boost circuit depends on the difference value between the charging voltage and the output voltage of the charger, for example, the output voltage of the charger is 400V, and the charging voltage is 800V, so that the boost amplitude is 400V, and in this way, the charging requirement of the rechargeable battery can be satisfied.
Referring to fig. 2, an embodiment of the present invention provides a charging system, as shown in fig. 2, the charging system 100 includes a charger 10 and an automobile charging system 20, wherein the automobile charging system 20 includes a boost circuit 21 and a rechargeable battery 22. The booster circuit 21 includes a positive input terminal 21A, a negative input terminal 21B, a positive output terminal 21C, and a negative output terminal 21D.
Specifically, as shown in fig. 3, the charger 10 includes a power supply circuit 11 for outputting a preset dc voltage, a dc output contactor K1, a dc output contactor K2, and a charger interface 10A for connecting with the vehicle charging system 20.
The vehicle charging system 20 further includes a first switch K3, a second switch K4, and a vehicle charging system interface 20A for connecting with the charger 10A. One end of the first switch K3 is electrically connected to the positive electrode of the charger 10 through the switch K1, the other end of the first switch K3 is connected to the positive input end 21A of the booster circuit 21, one end of the second switch K4 is electrically connected to the negative electrode of the charger 10 through the switch K2, and the other end of the second switch K4 is connected to the negative input end 21B of the booster circuit 21.
In the process of performing the IMD detection logic before and after charging, the working states of the first switch K3 and the second switch K4 on the automobile charging system 20 are matched with the dc output contactor K1 and the dc output contactor K2 on the charger 10, so as to achieve the detection of the charger IMD/the automobile IMD before starting charging, the detection of the charger IMD/the automobile IMD after starting charging, and the like under various charger standards, and the first switch K3 and the second switch K4 can also be used as nodes for starting charging and closing after the precharge in some standard charging systems, such as CCS2/CHAdeMO/ChaoJi standard charging systems. Because the car charging system 20 has compatibility problem after the boost circuit 21 is added, the car charging system 20 can be compatible with the current mainstream charger standard by the first change-over switch K3 and the second change-over switch K4, and can be compatible with the existing charging control logic while meeting the safety requirement of the car charging system.
In some embodiments, as shown in fig. 4, the automobile charging system 20 further includes a third switch K5, a fourth switch K6, a first fuse F1, and a second fuse F2. One end of the third switch K5 is connected to the positive input end 21C of the booster circuit 21, the other end of the third switch K5 is connected to the positive electrode of the rechargeable battery 22 through the first fuse F1, one end of the fourth switch K6 is connected to the negative output end 21D of the booster circuit 21, and the other end of the fourth switch K6 is connected to the negative electrode of the rechargeable battery 22 through the second fuse F2.
By timely opening the third and fourth switches K5 and K6 when a short circuit or an overcurrent fault occurs outside the rechargeable battery 22, the safety and reliability of the charging and discharging process of the rechargeable battery 22 can be improved, the first and second fuses F1 and F2 can realize overheat protection at the end of the rechargeable battery 22, and the safety and reliability of the charging process can be further improved.
In the existing charging system, the insulation characteristics of positive and negative direct current buses to the ground are detected through insulation impedance detection in the initialization and charging processes, IMD detection is performed during charging, which is a key operation for ensuring the safety of the charging system, and the insulation performance is affected by various factors to generate uncertain change, for example, the insulation performance is rapidly reduced in a damp environment, so that the IMD detection is required during charging, the insulation resistance of the positive and negative direct current buses to the ground is monitored in real time, and if the insulation resistance is abnormal, the charging process can be timely found out and stopped, thereby ensuring the safety of the charging process. It can be seen that the detection of insulation resistance by using IMD is the most important technical guarantee of the safety of the charging safety system, and thus, it is very important to ensure the accuracy of insulation resistance detection.
However, after the boost circuit 21 is added, the insulation resistance of the positive and negative dc buses to the ground also changes, and when the insulation resistance is detected later, zero condition of the detected voltage may occur or occurs, at this time, the insulation resistance of the positive and negative dc buses to the ground, which is obtained based on the unbalanced bridge theory shown in fig. 1, will occur, and once the pole appears, the deviation between the detected insulation resistance and the actual insulation resistance is very large, which may cause the failure risk of the existing IMD detection circuits of the charger and the electric automobile, and at the same time, may cause the system of the rechargeable battery high-voltage battery pack downward compatible with the voltage charger to fail to work normally. Therefore, how to ensure the accuracy of IMD detection based on the unbalanced bridge theory during charging in the application of adding a boost circuit into a charging system becomes a problem to be solved.
In view of the above, an embodiment of the present invention provides an insulation detection design method for an automobile charging system facing a boost circuit, as shown in fig. 3, the automobile charging system 20 includes a boost circuit 21 and a rechargeable battery 22, an output end of the boost circuit 21 is electrically connected with the rechargeable battery 22, and an input end of the boost circuit 21 is electrically connected with a charger. In this embodiment, by considering the influence of the insulation impedance to ground on the IMD detection in the subsequent charging when the boost circuit 21 is added, the accuracy of the IMD detection in the subsequent unbalanced bridge theory is ensured, so that the insulation impedance obtained by detection is very close to the actual insulation impedance, which is beneficial to improving the safety and reliability of the whole charging system.
As can be seen from the IMD detection based on the unbalanced bridge theory, a key factor in detecting to obtain accurate insulation resistance is that the voltage Ux and the voltage Uy cannot have zero points, but the reasons why the voltage Ux and the voltage Uy have zero points need to be analyzed in order to avoid the zero points.
As shown in fig. 5, an embodiment of the present invention provides an insulation detection design method for an automobile charging system facing a boost circuit.
In this method, first, the first equivalent resistance R1 of the positive input terminal 21A of the booster circuit 21 to the ground needs to be selected in advance, the second equivalent resistance R2 of the negative input terminal 21B of the booster circuit 21 to the ground needs to be determined in advance, and the third equivalent resistance R3 of the negative output terminal 21D of the booster circuit 21 to the ground.
Then, the boost voltage of the boost circuit 21 is determined, and the influence of the resistance value of the fourth equal resistor R4 of the positive output terminal 21C of the boost circuit 21 to the ground on the first voltage U1 and the second voltage U2 is detected through a simulation experiment, wherein the first voltage U1 is the voltage across the first equivalent resistor R1, and the second voltage U2 is the voltage across the second equivalent resistor R2.
Specifically, the cut-in resistor R0 is connected to two ends of the first equivalent resistor R1, meanwhile, the voltage of two ends of the first equivalent resistor R1 is measured to obtain the first voltage U1, the cut-in resistor R0 is connected to two ends of the second equivalent resistor R2, meanwhile, the voltage of two ends of the second equivalent resistor R2 is measured to obtain the second voltage U2, and the input voltage Uin is known, and then, the cut-in resistor R0 is known, the following formula can be obtained according to the circuit principle:
taking the impedance Z1 as the insulation impedance of the positive dc bus to ground and the impedance Z2 as the insulation impedance of the negative dc bus to ground, then, based on the unbalanced bridge principle, the following formula is obtained:
the above formula is added to a simulation experiment, and the simulation experiment uses the resistance value of the fourth equivalent resistor R4 as a variable, and performs simulation calculation on the above formula 3, formula 4, formula 5 and formula 6, and the simulation calculation may be performed based on any suitable simulation tool, for example, a simulation calculation based on MATHCAD.
In the process of pre-selecting the resistance value of the first equivalent resistor R1, the resistance value of the second equivalent resistor R2 and the resistance value of the third equivalent resistor R3 of the positive input end 21A, the negative input end 21B and the negative output end 21D of the boost circuit 21, respectively, the resistance values of the first equivalent resistor R1, the second equivalent resistor R2 and the third equivalent resistor R3 are all the resistance values meeting the preset positive and negative direct current bus insulation resistance to ground test standard of the automobile charging system 20. Under the test standard, the resistance values of the first equivalent resistor R1, the second equivalent resistor R2 and the third equivalent resistor R3 are all within a preset range, and any appropriate value can be selected as the resistance value of the first equivalent resistor R1, the second equivalent resistor R2 and the third equivalent resistor R3 within the preset range. Here, in combination with the judgment result of engineering experience, the resistance value of the first equivalent resistor R1 is 2mΩ (megaohm, 6 th order ohm of 10), the resistance value of the second equivalent resistor R2 is 2mΩ, and the resistance value of the third equivalent resistor R3 is 20mΩ.
Meanwhile, assuming that the cut-in resistor R0 is open (the resistor tends to infinity), the input voltage Uin is 400V, and the boost voltage Uboost is 400V, the simulation result is shown in fig. 6.
As can be seen in fig. 6, when the resistance of the fourth equivalent resistor R4 is equal to the resistance of the second equivalent resistor R2 and the third equivalent resistor R3 connected in parallel, the zero point appears in the first voltage U1, and as can be seen from the above formula 6, when the zero point appears in the first voltage U1, the pole appears in the impedance Z2 of the negative dc bus to the ground, which is extremely disadvantageous for the accuracy of the subsequent IMD detection.
In order to avoid the zero condition of the first voltage U1 or the second voltage U2 or the pole condition of the impedance Z1 or the impedance Z2, in this embodiment, according to the result of the simulation experiment, the range of the resistance value of the fourth equivalent resistor R4 is determined when the first voltage U1 and the second voltage U2 are not zero.
According to the result of the simulation experiment, the resistance value of the fourth equivalent resistor R4 when the first voltage U1 or the second voltage U2 has zero point can be obtained, so that the value range of the fourth equivalent resistor R4 can be obtained when the first voltage U1 and the second voltage U2 are not zero. It is understood that when the input voltage Uin, the boost voltage Uboost, and the like change, it is known from the formulas 3 and 4 that the resistance of the fourth equivalent resistor R4 also changes when the first voltage U1 or the second voltage U2 has a zero point, but once the resistance of the fourth equivalent resistor R4 when the first voltage U1 or the second voltage U2 has a zero point is determined, the range of the resistance of the fourth equivalent resistor R4 when the first voltage U1 and the second voltage U2 are not zero may also be determined according to the result of the simulation experiment. Therefore, when some conditions change, the value range of the fourth equivalent resistor R4 can be obtained according to the method.
Finally, selecting the resistance value of the fourth equivalent resistor R4 in the value range.
Specifically, in the process of selecting the resistance value of the fourth equivalent resistor R4 in the value range of the fourth equivalent resistor R4, according to the result of the simulation experiment, the resistance value of the fourth equivalent resistor R4 corresponding to the maximum voltage of the first voltage U1 and the second voltage U2 deviating from the zero point is obtained as the resistance value of the final fourth equivalent resistor R4.
As shown in fig. 6, in the simulation result, the first voltage U1 has a zero point, but the second voltage U2 has no zero point, and when the resistance value of the fourth equivalent resistor R4 is larger, the first voltage U1 deviates from the zero point, and when the resistance value of the fourth equivalent resistor R4 corresponding to the voltage with the first voltage U1 deviating from the maximum zero point is taken as the resistance value of the final fourth equivalent resistor R4, the change of the impedance Z1 and the impedance Z2 is extremely small, and an accurate detection result can be obtained when the IMD detection is performed subsequently. Since the voltage of the first resistor U1 is a maximum voltage that increases and slowly changes with the resistance value of the fourth equivalent resistor R4, when the rate of change of the voltage is smaller than the preset threshold value, the voltage can be considered to have reached the maximum voltage, and the maximum voltage is taken as a maximum voltage of the first voltage U1 and the second voltage U2 that deviates from the zero point.
Therefore, through a simulation experiment, the influence of the resistance value of the fourth equivalent resistor R4 on the first voltage U1 and the second voltage U2 can be effectively detected, and according to the result of the simulation experiment, the resistance value of the fourth equivalent resistor R4 is selected, and the selected resistance value of the fourth equivalent resistor R4 excludes the condition that the first voltage U1 and the second voltage U2 are zero, so that in the IMD detection based on the unbalanced bridge principle in the subsequent charging process, the IMD detection accuracy can be ensured.
In order to verify the validity of the resistance value of the fourth equivalent resistor R4 selected by the above method, the verification result is analyzed as follows with reference to fig. 7 and 8.
In fig. 7, the influence of the first equivalent resistance R1 on the impedance Z1 and the impedance Z2 is examined with the first equivalent resistance R1 as a variable. As can be seen from the simulation result in fig. 7, the values of the impedance Z1 and the first equivalent resistor R1 are changed linearly, the simulated calculated value of the impedance Z1 coincides with the value R1 of the first equivalent resistor to be measured, and the value of the impedance Z2 does not change with the change of the value of the first equivalent resistor R1, which indicates that the resistance value of the fourth equivalent resistor R4 selected by the above method is effective, so that the detected values of the impedance Z1 and the impedance Z2 can be close to the actual values of the impedance Z1 and the impedance Z2 when the IMD detection is performed subsequently, and the original IMD strategy of the charger is not affected.
In fig. 8, the influence of the second equivalent resistance R2 on the impedance Z1 and the impedance Z2 is examined with the second equivalent resistance R2 as a variable. As can be seen from the simulation result in fig. 8, the resistance values of the impedance Z2 and the second equivalent resistor R2 are linearly changed, the simulated calculated value of the impedance Z2 coincides with the value of the second equivalent resistor R1 to be measured, and the value of the impedance Z1 does not change with the change of the value of the second equivalent resistor R2, which indicates that the resistance value of the fourth equivalent resistor R4 selected by the above method is effective, so that the detected values of the impedance Z1 and the impedance Z2 can be close to the actual values of the impedance Z1 and the impedance Z2 when the IMD detection is performed subsequently, and the original IMD strategy of the charger is not affected.
Therefore, because the influence of the adding of the boost circuit 21 on the ground equivalent resistance on the subsequent IMD detection based on the unbalanced bridge principle is considered, and the resistance value of the positive output end of the boost circuit 21 corresponding to the zero point maximum voltage deviation of the first voltage U1 and the second voltage U2 is selected, the downward compatibility of the high-voltage battery pack with the charger can be realized, and the risk of failure of IMD detection caused after the boost circuit 21 is added can be effectively avoided.
It can be understood that when the IMD detection is actually performed, for example, when the first voltage U1 and the second voltage U2 are measured, there is often a measurement error, if the measurement error is not considered when the boost circuit is added, the value range of the fourth equivalent resistor R4 selected by the method is not accurate enough, so that an insulation impedance detection value almost consistent with the actual insulation impedance cannot be obtained in the subsequent IMD detection, therefore, on the basis of the method, an error coefficient is introduced to simulate the measurement error generated in the actual IMD detection, so as to obtain an accurate value range of the fourth equivalent resistor R4, and facilitate the subsequent selection of a more accurate value of the fourth equivalent resistor R4.
First, an error coefficient is determined. For example, when the error coefficient is 1%, the first voltage U1 and the second voltage U2 are adjusted and a simulation experiment is performed, and it is understood that in the simulation experiment, the first voltage U1 and the second voltage U2 are measured values obtained by taking measurement errors into consideration on the basis of actual measured values.
In the process of determining the value range of the resistance value of the fourth equivalent resistor R4 when the first voltage U1 and the second voltage U2 are not zero according to the results of the simulation experiment, the results of the simulation experiment are corrected according to the error coefficients by introducing the error coefficients, and the value range of the fourth equivalent resistor R4 is determined to be more accurate when the first voltage U1 and the second voltage U2 are not zero according to the corrected results of the simulation experiment, so that the resistance value of the fourth equivalent resistor R4 is better selected in the value range.
In order to facilitate real-time monitoring of insulation resistances of the positive and negative direct current buses to ground, respectively, and timely finding insulation faults, the embodiment of the invention provides an automobile charging system 20 which further comprises an insulation resistance detection circuit.
The insulation resistance detection circuit comprises a first detection unit, a second detection unit and a controller. The first detection unit may be used to detect a first voltage U1 across the first equivalent resistor R1, and the second detection unit may be used to detect a second voltage U2 across the second equivalent resistor R2.
The controller is respectively connected with the first detection unit and the second detection unit, the connection mode can be wired connection or wireless connection, and the controller can respectively acquire data of the first voltage U1 detected by the first detection unit and data of the second voltage U2 detected by the second detection unit.
Specifically, as shown in fig. 9, the first detection unit includes a first voltage detection circuit, a first switching resistor R01 and a fifth switching switch K7, the first voltage detection circuit and the fifth switching switch K7 are connected to the controller, the first switching resistor R01 is connected in series with the first non-switching switch K7 and then connected in parallel with the first equivalent resistor R1, and the first voltage detection circuit detects the first voltage U1 and transmits the first voltage U1 data to the controller. In some embodiments, the resistance of the first resistor R01 is adjustable, and by changing the resistance of the first resistor R01, multiple sets of data can be obtained, and by averaging the results, the results are more accurate.
As shown in fig. 9, the second detection unit includes a second voltage detection circuit, a second switching resistor R02 and a sixth switch K8, wherein the second voltage detection circuit and the sixth switch K8 are connected to the controller, the second switching resistor R02 and the sixth switch K8 are connected in series and then connected in parallel to the second equivalent resistor R2, and the second voltage detection circuit detects the second voltage U2 and transmits the second voltage U2 data to the controller. In some embodiments, the resistance of the second cutting resistor R02 is adjustable, and by changing the resistance of the second cutting resistor R02, multiple sets of data can be obtained, and by averaging the results, the results are more accurate.
The controller can control the working states of the fifth change-over switch K7 and the sixth change-over switch K8, obtain the corresponding values of the first voltage U1 or the second voltage U2, namely, obtain the value of the first voltage U1 when the fifth change-over switch K7 is closed and the sixth change-over switch K8 is opened, and obtain the value of the first voltage U1 when the fifth change-over switch K7 is opened and the sixth change-over switch K8 is closed, in this way, the insulation impedance Z1 of the positive direct current bus to the ground and the insulation impedance Z2 of the negative direct current bus to the ground can be obtained through calculation by establishing a related formula, and therefore the insulation impedance is monitored.
Finally, it is to be noted that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, which are not to be construed as additional limitations on the scope of the invention, but rather as providing for a more thorough understanding of the present invention. And under the idea of the invention, the technical features described above are continuously combined with each other, and many other variations exist in different aspects of the invention as described above, which are all considered as the scope of the description of the invention; further, modifications and variations of the present invention may be apparent to those skilled in the art in light of the foregoing teachings, and all such modifications and variations are intended to be included within the scope of this invention as defined in the appended claims.
Claims (9)
1. The utility model provides an insulation detection design method of car charging system towards boost circuit, car charging system includes rechargeable battery, boost circuit, first detecting element, second detecting element and controller, boost circuit's output with rechargeable battery electricity is connected, boost circuit's input is used for being connected with the charger electricity, first detecting element is used for detecting the first voltage at first equivalent resistance both ends, second detecting element is used for detecting the second voltage at second equivalent resistance both ends, the controller is connected with respectively first detecting element and second detecting element, is used for obtaining first voltage and the data of second voltage, its characterized in that, the method includes:
the method comprises the steps of selecting a resistance value R1 of a first equivalent resistor of a positive input end of the booster circuit to the ground equivalent resistor in advance, connecting a cut-in resistor R0 at two ends of the first equivalent resistor R1, and simultaneously measuring voltages at two ends of the first equivalent resistor R1 to obtain a first voltage U1;
the resistance value R2 of a second equivalent resistor of the negative input end of the booster circuit to the ground is selected in advance, the two ends of the second equivalent resistor R2 are connected into a cut-in resistor R0, and meanwhile, the voltages at the two ends of the second equivalent resistor R2 are measured to obtain a second voltage U2; the method comprises the steps of,
the resistance R3 of the third equivalent resistor of the negative output end of the booster circuit to the ground;
determining a boost voltage Uboost of the boost circuit;
the input voltage Uin is known, the cut-in resistance R0 is known, and the following formula is obtained according to the circuit principle:
taking the impedance Z1 as the insulation impedance of the positive dc bus to ground and the impedance Z2 as the insulation impedance of the negative dc bus to ground, then, based on the unbalanced bridge principle, the following formula is obtained:
adding the formula into a simulation experiment, and detecting the influence of the resistance R4 of the fourth equivalent resistor of the positive output end of the booster circuit to the ground equivalent resistor on the first voltage U1 and the second voltage U2 through the simulation experiment;
according to the result of the simulation experiment, determining the value range of the fourth equivalent resistor R4 when the first voltage U1 and the second voltage U2 are not zero;
selecting the resistance value of the fourth equivalent resistor R4 in the value range;
and the insulation impedance Z1 of the positive direct current bus to the ground and the insulation impedance Z2 of the negative direct current bus to the ground are calculated by establishing a related formula, so that the insulation impedance is monitored.
2. The insulation detection design method according to claim 1, wherein the step of selecting the resistance value of the fourth equivalent resistor in the value range further comprises:
and selecting the resistance value of a fourth equivalent resistor corresponding to the maximum voltage of the first voltage and the second voltage deviating from the zero point within the value range according to the result of the simulation experiment.
3. The insulation detection design method according to claim 1, further comprising:
determining an error coefficient;
correcting the result of the simulation experiment according to the error coefficient;
and determining the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero according to the result of the simulation experiment, wherein the step specifically comprises the following steps: and determining the value range of the fourth equivalent resistor when the first voltage and the second voltage are not zero according to the corrected simulation experiment result.
4. The insulation detection design method according to claim 1, wherein the resistance of the first equivalent resistor, the resistance of the second equivalent resistor and the resistance of the third equivalent resistor are all values satisfying the preset insulation resistance to ground test standard of the automobile charging system.
5. The insulation detection design method according to claim 1, wherein the automobile charging system further comprises a first change-over switch and a second change-over switch;
one end of the first change-over switch is used for being electrically connected with the positive electrode of the charger, and the other end of the first change-over switch is electrically connected with the positive input end of the boost circuit;
one end of the second change-over switch is used for being electrically connected with the negative electrode of the charger, and the other end of the second change-over switch is electrically connected with the negative input end of the boost circuit.
6. The insulation detection design method according to claim 1, wherein the automobile charging system further comprises a third change-over switch and a fourth change-over switch;
one end of the third change-over switch is electrically connected with the positive output end of the boost circuit, and the other end of the third change-over switch is electrically connected with the positive electrode of the rechargeable battery;
one end of the fourth change-over switch is electrically connected with the negative output end of the boost circuit, and the other end of the fourth change-over switch is electrically connected with the negative electrode of the rechargeable battery.
7. The insulation detection design method according to claim 1, wherein the automobile charging system further comprises a first fuse and a second fuse;
one end of the first fuse is electrically connected with the positive input end of the booster circuit, and the other end of the first fuse is electrically connected with the positive electrode of the rechargeable battery;
one end of the second fuse is electrically connected with the negative input end of the boost circuit, and the other end of the second fuse is electrically connected with the negative electrode of the rechargeable battery.
8. The insulation test design method according to claim 1, wherein,
the first detection unit comprises a first voltage detection circuit, a first switching resistor and a first change-over switch;
the first voltage detection circuit and the first change-over switch are connected with the controller, the first switching-in resistor and the first change-over switch are connected in series and then connected with the first equivalent resistor in parallel, and the first voltage detection circuit is used for detecting the first voltage and transmitting the first voltage data to the controller.
9. The insulation test design method according to claim 1, wherein,
the second detection unit comprises a second voltage detection circuit, a second cut-in resistor and a second change-over switch;
the second voltage detection circuit and the second change-over switch are connected with the controller, the second cut-in resistor and the second change-over switch are connected in series and then connected with the second equivalent resistor in parallel, and the second voltage detection circuit is used for detecting the second voltage and transmitting the second voltage data to the controller.
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